The present invention relates to an apparatus for controlling resist stripping solution used in stripping resist in a semiconductor manufacturing process, a liquid crystal board manufacturing process or the like, and more particularly to an apparatus combining a continuous automatic replenishing mechanism of resist stripping solution in cyclic use, a water concentration regulating mechanism, and a resist stripping solution automatic discharge mechanism for arresting deterioration of resist stripping performance due to enrichment of dissolved resist.
The resist material used for a photolithography in a semiconductor manufacturing process, a liquid crystal manufacturing process or the like, is divided into a positive type which has solubility by exposure and a negative type which has insolubility by exposure. The positive type resist is used mainly.
As a typical example of the positive type resist, a resist mainly comprises a naphthoquinone-diazido photosensitive agent and an alkali soluble resin (novolak resin).
At the final stage of a photolithography process, a process for completely removing the resist from the board must be installed.
Japanese Laid-Open Patent Publication No. 7-235487 discloses an apparatus for controlling a resist stripping solution comprising resist stripping solution discharge means for discharging resist stripping solution by detecting the dissolved resist concentration in the resist stripping solution by means of an absorption photometer, first replenishing means for replenishing organic solvent and alkanolamine, or a fresh resist stripping solution preliminaly blending organic solvent and alkanolamine by detecting the liquid level of the resist stripping solution by means of a liquid level gauge, and second replenishing means for replenishing at least one of organic solvent and alkanolamine by detecting the alkanolamine concentration of the resist stripping solution by means of an absorption photometer.
In the resist stripping process of a liquid crystal board, as mentioned above, a blending solution of organic alkali and organic solvent is mainly used as a resist stripping solution, and it is found that a superior effect is obtained by using a resist stripping solution further adding an appropriate amount of water.
That is, by employing a resist stripping solution containing an appropriate amount of water, the board processing temperature may be lowered to about 40.degree. C. from about 80.degree. C. in the case of a resist stripping solution not containing water, and therefore damage to the foundation metal for forming a board or a semiconductor circuit can be decreased. The resist stripping solution can be handled as nonflammable matter and safety is high, the evaporation loss is mainly water which is inexpensive, and the stripping speed is high.
For example, a solution of dimethyl sulfoxide source solution and pure water, a solution of N-methylpyrrolidone source solution and pure water, a solution of alkanolamine, glycolether and pure water or the like is used in a spray method or a dip method.
In the conventional method, starting by filling a resist stripping processing tank with the specified volume of a fresh resist stripping solution at the specified concentration, when the resist stripping solution is consumed and reaches a specified deterioration concentration region, on the basis of an empirical index such as the number of boards processed, the entire volume is exchanged with a prepared fresh solution in the batch operation system. This solution exchanging frequency varies with the tank volume, the type of boards and number of the boards, etc., but it is generally done about every four days.
When the resist stripping solution is deteriorated, the stripping speed is not constant, the remainder of the resist stripping is broken out, and decline in yield occurs. The amount of loss is significant when defectives occur in the resist stripping process which is the final stage in a photolithography process.
A resist stripping solution containing water is usually used in the temperature range of 30 to 60.degree. C.
With regard to the boiling point of the components used for a resist stripping solution, organic alkali or organic solvent is about 160 to 250.degree. C., and water is 100.degree. C.
Accordingly, the water concentration is lowered as the water of a lower boiling point vaporizes preferentially with a purge nitrogen gas for air seal to the resist stripping solution tank during operation, and then the concentration variation of the resist stripping solution occurs. As a result, the resist stripping performance declines, but conventionally the water concentration was not measured in real time and not controlled at a specified concentration.
When the water concentration is further lowered, it may come to have a flash point, which leads to the risk of an explosion.
Besides, the resist dissolved in the resist stripping solution in the resist stripping process is gradually enriched, and it is a dominant cause of resist stripping performance deterioration such as a decline in stripping speed and occurrence of the remainder of the resist stripping, but conventionally the dissolved resist concentration was not measured in real time and not controlled at a specified concentration.
Therefore, in this period, the water concentration and the dissolved resist concentration vary with the passing of time and are not constant, and the remainder of the resist stripping is broken out. It was hence difficult to control the delicate dimensional precision in the liquid crystal boards, the product quality was unstable, and the yield was lowered.
Besides, due to stopping (down time) for exchanging solution, the operation rate was significantly lowered, and the exchange work of the resist stripping solution required extra labor cost.